Prune tree named ‘D6N-72’

ABSTRACT

A new prune cultivar designated ‘D6N-72’ has been developed. The new cultivar is the result of a cross between ‘Improved French’ and ‘Tulare Giant.’ The fruit of this cultivar are large, light purple to light bluish purple in color and covered with a grayish waxy bloom. The ‘D6N-72’ tree is productive and a regular bearer.

FIELD OF THE INVENTION

Botanical/commercial classification: (Prunus domestica)/“French-type”prune variety.

Varietal denomination: cv. D6N-72.

BACKGROUND OF THE INVENTION

Prunes (dried plums) are a popular food item providing a good source ofvitamin C as well as other vitamins and nutrients for consumers. Assuch, there is a continued need to develop prune trees with increasedyield and quality of plums for the production of prunes.

The long term commercial success of “French-type” prunes, both theEuropean ‘Prune d'Ente’ and Burbank's ‘Improved French’, suggests thatthey will be desirable parents for new cultivars. However, there areseveral problems involved in incorporating these cultivars directly intoa breeding program. Relatively few seedlings from these cultivarsexpress substantial maturity spread, a major industry need. Seedlings of“French” origin are often weak in vigor and slow to come into bearing(up to eight years). These unproductive (juvenile) years greatly extendthe breeding cycle. In addition, most seedlings solely derived from thisparentage do not attain the level of production of the parent and have awide range of variability in adaptation to climatic conditions. Even thebest selections from France are generally not adapted to Californiaclimatic conditions.

Thus there is a tremendous need for developing new prune varietiesutilizing “French-type” prune trees in breeding where the resultingtrees that express precocity of bearing (shortened juvenility), spreadof maturity (both early and late), freedom from heat damage (in bothfruit and tree) and vigorous seedling growth.

SUMMARY OF THE INVENTION

In order to meet these needs, the present invention is directed to the‘D6N-72’ prune tree which is a new prune cultivar developed for thedried fruit market. It is of the plum species Prunus domestica. This newcultivar is the result of a controlled cross made between the Europeanplum/prune cultivars ‘Improved French’ and ‘Tulare Giant’ in March of1992. The cross was made between the prune cultivar ‘Improved French’used as the female (seed) parent and the plum cultivar ‘Tulare Giant’used as the male (pollen) parent. ‘Tulare Giant’ is the subject of U.S.Plant Pat. No. 12,224. ‘Improved French’ is not patented in the UnitedStates. Hybrid seed harvested from this cross at the end of the 1992growing season was given the family designation “P93.22” at plantingtime in spring of 1993. This family of seedlings, along with manyothers, was grown into small trees in a nursery at University ofCalifornia (UC), Kearney Agricultural Center at Parlier, Calif. (KAC)during 1993 and 1994. The trees were dug from the nursery at Kearney atthe end of the 1994 growing season and transplanted into a permanentseedling block at University of California, Davis in spring of 1995(Mar. 1, 1995). The seedling block was located within the Pomology fieldresearch area at University of California, Davis and was given thedesignation of “D Block”.

The ‘D6N-72’ prune cultivar first fruited on the original seedling inJuly of 1997. The first propagation of selection ‘D6N-72’ occurred in1998 in the prune selection block at the KAC. The KAC propagationsinvolved grafting onto two trees of six-year old ‘Marianna’ plumrootstock (not patented). A second propagation of a single tree of‘D6N-72’ was made in 1998 in a prune selection block at the UC WolfskillExperimental Orchard located near Winters, Calif. The propagation atWolfskill was made on ‘Marianna’ plum rootstock that was two years oldat the time. The trees grafted in 1998 produced fruit in 2000, attestingto the high degree of precocity of this new cultivar. The firstcommercial crop of fruit was produced on the propagated trees at Kearneyduring the 2001 growing season. The fruit produced on the propagatedtrees has been similar in all aspects to that produced on the originalseedling. The original propagules grafted in 1998 continued to producegood commercial crops in 2002 and 2003. The propagules are identical tothe original plant in all distinguishing characteristics so as toestablish that the claimed plant is stable.

In addition to the ‘Marianna’ plum rootstock, the new cultivar has alsobeen propagated onto ‘Myrobalan’ plum rootstock (not patented). Bothplum stocks have produced vigorous, healthy and productive trees. Growertest sites were developed for this selection, beginning in 2001 andthereafter, both in the Sacramento and San Joaquin Valleys ofCalifornia. Field test evaluations have been successful and indicatesubstantial commercial potential for the new variety.

In comparison with the seed parent ‘Improved French’, which is theindustry standard, ‘D6N-72’ flowers approximately two weeks earlier.Additionally, the date of fruit maturity for ‘D6N-72’ in a normal yearis early August, approximately 13 days ahead of ‘Improved French’. Thefruit is large, light purple to light-bluish purple in color and coveredwith a grayish waxy bloom. The fruit is oval in shape. In early tests,the fruit was substantially larger than ‘Improved French’ at fullmaturity. For the French Prune, individual fruit weight ranges from 23.0to 35.0 grams, whereas ‘D6N-72’ fruit ranges from 35.0 to 47.0 grams,depending on the crop load on the tree. The fruit stone is nearly freeand pits easily.

The ‘D6N-72’ tree is slightly more vigorous than ‘Improved French’, itis productive and is a regular bearer. The ‘D6N-72’ prune has beensuccessfully propagated on ‘Marianna’ plum rootstock with good results,however it is not recommended that it be grafted on peach rootstockswithout significant pre-testing as many other Prunus domestica cultivarsare incompatible with peach. Fruit of the ‘D6N-72’ cultivar dries into avery high quality prune with an excellent, fruity flavor. Fresh fruitquality is also excellent with relatively low acidity. For optimumquality fresh fruit should not be picked with less than 19 degrees Brix.

In comparison with the pollen parent ‘Tulare Giant’, ‘D6N-72’ flowers atabout the same time, however, it produces a fruit much more suited todrying than does the pollen parent ‘Tulare Giant,’ which is a freshstyle market prune. ‘D6N-72’ is also self-fertile, while ‘Tulare Giant’needs a pollinator. Additionally, the fruit of ‘D6N-72’ is smaller than‘Tulare Giant.’ For ‘D6N-72,’ individual fruit weight ranges from 35.0to 47.0 grams, whereas for ‘Tulare Giant,’ fruit weight ranges from 44.0to 78.0 grams, depending on the crop load on the tree. The fruit of‘D6N-72’ is also lighter in color and matures at least one week laterthan ‘Tulare Giant.’

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows ‘D6N-72’ fruit samples. Side and top views of the fruit areshown. In addition, views of sliced fruit and an isolated pit are shown.

FIG. 2 shows branches of ‘D6N-72’ trees with and without fruit. Slicedand whole fruit samples are also shown.

BOTANICAL DESCRIPTION OF THE PLANT

The following horticultural description was prepared from plant materialand fruit obtained from a pair of six-year old grafted trees of thesubject new cultivar located at the University of California KearneyAgricultural Center (KAC), 9240 S. Riverbend Avenue, Parlier, FresnoCounty, Calif. 93648 USA. The plant material was observed during the2002 and 2003 growing seasons. Descriptions are provided below. Colordefinitions used in this description are from “The Royal HorticulturalSociety Colour Chart,” 3^(rd) edition, published in 1995.

Tree

The genus and species of the subject new cultivar is Prunus domestica.This species is popularly known as “European plum.” Individual cultivarsof this plum species that are high in sugar content and can dry withoutfermentation have historically been designated as “prunes.” Currentnomenclature within the industry now refers to this type of high-sugarplum as a “dried plum” or a prune. The tree of the subject new cultivaris above average in vigor and hardy under normal San Joaquin Valley,Calif. climatic conditions. Tree form is upright to upright-spreading.At the end of the 2002 growing season, the subject trees were pruned toa height of approximately 3.7 meters, with approximately 1.5 to 2.1meters of growth removed at the time of pruning. Tree width across thecrown of the tree is approximately 4.3 meters. The trees have beenmaintained by pruning in an open-vase training system. The subject treeswere propagated on ‘Marianna’ plum rootstock. Scions of the ‘D6N-72’cultivar, obtained from the original seedling at University ofCalifornia Davis, were placed on the ‘Marianna’ at Kearney in spring of1998. A small crop of fruit was produced on the grafted tree in the 2000growing season, with the first full crop produced in 2001. Fruitproduced on the propagated trees was identical to the fruit produced onthe original seedling in all aspects. Tree spacing at the Kearney testorchard is 5.49 meters (18 feet) between the rows by 4.88 meters (16feet) down the row. The new cultivar has been very productive,precocious and a regular bearer.

Trunk

The lower portion of the trunk of the subject trees is made up of the‘Marianna’ rootstock. At 20 cm above the surface of the ground, thestock varies from 19.5 to 20.0 cm in diameter. The varietal top isgrafted onto the stock at a height ranging from 50.9 to 60.6 cm abovethe surface of the ground. From 4 to 6 scaffolds arise from the level ofthe multiple graft union. These primary scaffolds range from 7.5 to 14.0cm in diameter at the base of the scaffold. The bark surface of thescaffolds is moderately smooth except for the roughened surfaces of thenumerous bark lenticels. Bark color is grayish (Fan #4, Sheet 201-B).The bark lenticels are roughly oval in shape and flattened horizontally.Lenticel width ranges from approximately 2 to 7 mm, with occasionallenticels even wider. Lenticel height varies from 1.5 to 3.0 mm. Thelenticel surface is roughened and calloused. Color of the lenticelsurface callous tissue is a light brown-tan (Fan #4, Sheet 164-B).

Branches

The tree branches are average to slightly above average in thickness forthe species. The surface of 2-year-old and older branches is glabrous.Bark lenticels are relatively numerous over the surface of these olderbranches, causing some roughening of the branch surface. A moderateamount of scarfskin can be present. The color of 2-year-old and olderbranches is a medium grey (Fan #4, Sheet 201-C). Surface texture ofcurrent season's shoots is quite smooth and glabrous. The color of theseyoung shoots is a pale to medium green (Fan #3, Sheet 138-C and Fan #3,Sheet 138-B). Color becomes more brownish as the shoot matures (Fan #4,Sheet 177-A, Fan #4 Sheet 200C, Fan #4 Sheet 200D and Fan #4, Sheet200-B). Young shoots exposed to sunlight can exhibit shades of red andviolet (Fan #2, Sheet 59-C and Fan #4, Sheet 187-A). Shoot internodelength is normal for the species, ranging from 20 to 36 mm in length onfruiting hanger branches measured from node to node. The color of newexpanding shoot tips is a medium green (Fan #3, Sheet 146-C), withbronze coloration overlying the green in some locations (Fan #4, Sheet163-A).

Leaves

General leaf size is medium to large. Measurements have been taken fromleaves growing on vigorous, upright, current season's shoots. Leaflength ranges from 10.4 to 14.1 cm and leaf width from 4.7 to 6.3 cm.Leaf thickness is average. Leaf surfaces are slightly rugose.

Leaf Form

Leaf form is variable, from oval to slightly obovate. Leaf apex form isacute, but at times only slightly so. The leaf apex is often twistedsideways. Leaves on spurs and small shoots are smaller and more variablein form, ranging from fully obovate to nearly lanceolate. The uppersurfaces of the leaf are essentially glabrous. On the lower side of theleaf, the interveinal areas are glabrous. Surfaces of the veins arepubescent. The primary mid-vein is heavily pubescent, with an abundanceof medium length hairs.

Leaf Color

Color of the upper leaf surface is dark green (Fan #3, Sheet 137-A).Color of the lower leaf surface is a grey-green (Fan #3, Sheet 138-B).Color of the primary mid-vein on the under side of the leaf is a palegreen (Fan #3, Sheet 147-D).

Leaf Margins

Leaf margin form is crenate. The crenations are large and somewhatirregular. The leaf margins are moderately undulate.

Leaf Petiole

The leaf petiole is of average size. Petiole length is rather variable,from 14 to 25 mm. Petiole thickness ranges from 1.0 to 1.5 mm, measuredat mid-petiole. Color of the petiole is a pale green (Fan #3, Sheet147-D). Some petioles are slightly darker green, especially in thepetiole groove area (Fan #3, Sheet 148-C). Petiole surfaces arepubescent, more highly so within the petiole groove and along the tworidges subtending the petiole groove.

Leaf Glands

The leaf glands are small and variable, most frequently globose but attimes weakly reniform. Diameter of the glands can range from 0.5 to 1.5mm. Glands usually do not occur on the leaf petiole itself but ratherare present on short stalks along the very base of the leaf margins.Glands are variable in number from none to 2, most frequently 2. Glandposition is alternate. Color of the young glands is a yellow-green (Fan#3, Sheet 144-C), with the glands becoming darker in color anddeteriorating with age.

Leaf Stipules

The leaf stipules are medium to large in size, from 6 to 10 mm at thebase of the larger leaves and ranging from 1.5 to 3.0 mm in width.Stipule form is usually linear lanceolate. Occasionally 1 or 2 lobes canbe present arising from the basal area of the stipule. These lobes canrange from 1.5 to 4.0 mm in length and are also linear lanceolate inform. Stipule margins are serrate and often cupped inwards. Color of thestipules is a light green (Fan #3, Sheet 138-C). Substantial numbers ofstipules are persistent throughout the growing season.

FRUIT DESCRIPTION

Maturity

The fruit of the new cultivar is described at full commercial maturity.Date of harvest in 2002 at the University of California KearneyAgricultural Center, Parlier, Fresno County, Calif. was Aug. 8approximately 13 days ahead of the common prune cultivar ‘ImprovedFrench’ which was harvested in the same location on Aug. 21 in 2002. Atthat time, fruit of the ‘D6N-72’ had an average flesh pressure of 4.0pounds and an average soluble solids content of 20.4 degrees Brix.Harvest was made all at one time as is the common commercial practice inCalifornia, where mechanical harvesting by shaker is the norm.

Fruit Size

Fruit size is generally large for a dried plum and quite uniform. Cheekdiameter varies from 37 to 45 mm, suture diameter from 36 to 44 mm andaxial diameter from 45 to 53 mm.

Fruit Weight

The individual fruit weight ranges from 35.0 to 47.0 grams, depending onthe crop load.

Fruit Form

The fruit is most frequently oval in form in lateral aspect, wellrounded both apically and basally. In apical aspect, the form variesfrom globose to slightly oval. The fruit halves can vary from fullysymmetrical to slightly asymmetrical.

Fruit Suture

The suture is a thin but distinct line, extending continuously from apexto base. Suture color is usually darker than the surrounding skinsurface. Color of the suture is a dark red-purple (Fan #2, Sheet 59-C,Fan #2, Sheet 59B and Fan #2, Sheet 59-A). Most frequently the suture isnot depressed, although occasionally, on a few fruit, a slightdepression can be observed. No stitching or callousing is present.

Ventral Surface

The ventral surface is usually smooth. Only an occasional fruit displaysa slight amount of lipping.

Stem Cavity

The stem cavity is very small. Cavity width varies from 3.0 to 6.0 mm,and cavity length varies from 8.0 to 11.0 mm. The cavity form is oval,tapering somewhat at the ventral suture end. Cavity depth ranges from3.0 to 4.0 mm.

Fruit Base

The base of the fruit is rounded and regular in form. The base angle isusually at a right angle to the fruit axis.

Fruit Apex

The fruit apex is quite smoothly rounded. Usually there is no depressionat the pistil point. The pistil point is apical. A small amount ofcallous is often present on the pistil point. The callous is tan-brownin color (Fan #4, Sheet 165-B).

Fruit Stem

The fruit stem is of medium length, ranging from 11 to 18 mm. Stemthickness ranges from 1.5 to 1.8 mm, measured at mid-stem. The fruitstem is essentially glabrous, although occasional scattered hairs can befound. Stem color is a pale green at commercial maturity (Fan #3, Sheet146-D).

Skin

The fruit skin is of average thickness and essentially glabrous. Theskin has very slight acidity and is tightly attached to the fruit fleshat commercial maturity. No tendency to crack or split has been observed.

Skin Color

The skin is light purple to light bluish-purple in color at commercialmaturity and with the grayish, waxy cuticle bloom intact (Fan #2, Sheet76-A, Fan #2, Sheet 85A, and Fan #2, Sheet 91-A). With the bloomremoved, the skin color is moderately uniform, usually in a washedpattern, and usually from 100 to 95 percent colored. Skin color can bereddish (Fan #4, Sheet 180-A) or darker purple (Fan #4, Sheet 187-A),with various ranges of hues in between. A yellow-amber ground colorationcan, at times, be present (up to 5% of the fruit surface). This groundcoloration is usually present near the basal end of the fruit or overthe basal shoulders (Fan #1, Sheet 23-B). Some yellow speckling ispresent over the basal shoulders, with the same coloration as the groundcolor (Fan #1, Sheet 23-B).

Flesh Color

Flesh color can vary from an amber-yellow (Fan #1, Sheet 15-B) to adarker amber-orange Fan #1, Sheet 26-A), with the darker colors in andnear the pit cavity. A moderate number of fibers are present throughoutthe flesh. These flesh fibers are light yellow in color (Fan #1, Sheet20-A).

Flesh Texture

At commercial maturity, the flesh is firm and relatively fine textured.The flesh becomes soft and juicy with advanced maturity.

Ripening

The fruit ripens evenly.

Flavor

Flavor of the ‘D6N-72’ fruit is sweet and mild, with a distinctivefruity flavor. The fruit has a relatively low acidity.

Aroma

Aroma is very slight to lacking at commercial maturity.

Eating Quality

Eating quality of the ‘D6N-72’ fruit is very good, especially when thesugar level reaches or exceeds 19 degrees Brix.

Processing Quality

From early observations and with similar crop loads, the ‘D6N-72’cultivar appears to develop larger sized fruit than that of the industrystandard dried plum, the ‘Improved French’. With similar crop loads, the‘D6N-72’ fruit appears to develop comparable sugar levels to those ofthe ‘Improved French’. Fruit of the new cultivar dries into anattractive, high quality dried plum or prune. The fruit stone of the‘D6N-72’ is nearly freestone and pits easily using the industry standard“Ashlock” mechanical pitter. The external appearance of the new ‘D6N-72’cultivar is similar to that of the ‘Improved French’ with the possibleexception of the ‘D6N-72’ having somewhat fewer, broader wrinkles. Driedflavor of the ‘D6N-72’ fruit is lighter than that of the ‘ImprovedFrench’, with a more complex fruity flavor.

STONE DESCRIPTION

Attachment

The stone is nearly free, with a small percentage of fruit having fibersthat cling to the stone surface.

Stone Size

The stone is medium in size. Stone length ranges from 28 to 32 mm andstone width ranges from 12 to 15 mm. Thickness of the stone ranges from7 to 9 mm.

Fibers

A few medium length fibers are attached to the stone surface, primarilyalong the surfaces of the stone sutures.

Stone Form

The predominant form of the stone is a long narrow oval.

Stone Base

The base of the stone is tapered and slightly truncate. The base angleis variable, from slightly oblique to fully at right angle to the stoneaxis.

Hilum

The hilum is small in size, from 1.5 to 2.0 mm in length and from 1.0 to1.5 mm in width. Form of the hilum is oval, but the scar issubstantially eroded. Distinct ridges and grooves occur over the neckarea of the hilum area, with the ridges converging basally.

Apex

The apex is generally rounded in form, but often with a very low blunttip. Significant pitting occurs over the apical shoulder along thedorsal edge. A slight amount of erosion can be present, usuallylaterally, near (or just below) the apex.

Stone Sides

The stone sides are almost always unequal or asymmetrical.

Stone Surface

The stone surfaces are usually relatively smooth laterally, withslightly netted, very low ridging. From 5 to 7 mm up from the stonebase, numerous distinct ridges and grooves are present, convergingbasally. Along the ventral suture from one (to occasionally two) deepgrooves are present, varying from continuous to occasionallydiscontinuous. The groove is usually located from 1 to 2 mm below theedge of the ventral suture (measured at mid-stone), running roughlyparallel to the ventral edge but converging both apically and basally.

Ventral Edge

The ventral edge is relatively broad and quite regular. The suturesurface can have several shallow grooves and occasionally a low wing canbe present.

Dorsal Edge

A single distinct groove is present along the dorsal edge. The groove isquite large from the base of the dorsal edge up to a distance of onequarter to one half of the total length of the dorsal edge, measuringfrom 1.0 to 1.5 mm in width at mid point. Above this wide groove, on upover the apical shoulder of the dorsal edge, the groove narrows and can,at times become discontinuous. Most frequently the groove at the upperapical edge location appears as only a thin line. A moderate amount ofpitting and erosion is present over the apical shoulder of the dorsaledge.

Stone Color

Color of the stone is variable, ranging from a tan color (Fan #4, Sheet165-C) when dry, to a darker brown (Fan #4, Sheet 165-B) when wet.

Tendency to Split

No tendency for the stone to crack, split or fragment has been observed.

Floral Description

The following floral description was obtained from plant materialgrowing on test trees of the ‘D6N-72’ cultivar located at the Universityof California Kearney Agricultural Center, Parlier, Calif. Thisdescription was developed during March of both 2002 and 2003. The numberof cold chilling hours (total hours below 45 degrees F.) for the 2001 to2002 winter season at Parlier was 1025 hours. This accumulation is aboutnormal to slightly high. The number of cold hours accumulated for the2002 to 2003 winter season at Parlier was 813 hours. This represents arelative warm winter. Because of the similarity of dates of bloom forthe ‘D6N-72’ cultivar in both years, it appears that the chillingrequirement of the new ‘D6N-72’ cultivar was fully satisfied at bothlevels of chilling.

Flower Buds

Size

The flower buds range from medium to small in size, from 2 to 3 mm inlength and from 1.0 to 1.5 mm in width.

Form

General bud form is slightly variable but most frequently conic andplump. The buds most often are moderately appressed to the bearingbranch. The flower buds are hardy under the normal climatic conditionsthat occur in the San Joaquin Valley of Central California.

Color

Bud color is a dark brown (Fan #4, Sheet 200-A).

Bud Surface

The lateral surfaces of the bud scales are essentially glabrous.

Bloom Timing

Bloom timing for the ‘D6N-72’ cultivar is early for the species. Date offirst bloom in 2002 was March 1 with full bloom occurring on Mar. 11 ,2002. Date of first bloom for the ‘D6N-72’ was Feb. 28 in 2003, followedby full bloom on Mar. 10, 2003. Date of full bloom for the ‘ImprovedFrench’ dried plum cultivar was Mar. 19 in 2003 approximately 9 daysafter full bloom of the ‘D6N-72’. Duration of bloom for the ‘D6N-72’ canrange up to 14 days. Date and duration of bloom for any cultivar can besubstantially impacted by the amount of chilling hours received in anyspecific year and the chilling requirement of the individual cultivar.

Flower Size

Flower size ranges from medium to large for the species. Diameter of theflower, fully expanded, varies from 23 to 27 mm.

Bloom Quantity

The quantity of bloom is abundant. The number of flower buds per noderanges from 1 to 2, most frequently 2.

Flower Petals

Flower petals are medium to large in size. Petals range from 10 to 12 mmin length and from 8 to 10 mm in width. Petal number is five. The petalform is variable, from oval to slightly obovate. Petal color is white(Fan #4, Sheet 155-D). The petal claw is truncate in form and quiteshort. The claw ranges from 1.0 to 1.5 mm in width, but only averages0.5 mm in length. The petal margins are moderately undulate and mostfrequently cupped inwards. Petal apices are variable, with the apex attimes smoothly rounded but not infrequently also found with a distinctnotch.

Flower Pedicel

Pedicel length ranges from 8 to 12 mm. Pedicel thickness ranges from 1.0to 1.5 mm measured at mid-pedicel. Color of the pedicel is ayellow-green (Fan #3, Sheet 144-C). The surface of the pedicel isglabrous.

Floral Nectaries

Color of the floral nectaries is a dull orange (Fan #4, Sheet 163-A),lightening with age to a dull yellow-green (Fan #3, Sheet 146-D).

Calyx

Surfaces of the calyx are slightly pubescent, with extremely short andvery fine hairs. Calyx color is a dull yellow-green when young (Fan #3,Sheet 152-C), becoming more greenish with age (Fan #3, Sheet 144-C).

Sepals

Sepal surfaces are generally slightly pubescent, with very short andfine hairs, except along the sepal margins where the pubescence islonger and more readily visible. The sepals are of average size, rangingfrom 4 to 5 mm in length and from 2.5 to 3.5 mm in width. The sepals aremost frequently ovate in form. Sepal color is green (Fan #3, Sheet144-C).

Anthers and Pollen

The anthers are average to slightly above average in size. Anther coloris a golden-yellow (Fan #1, Sheet 14-B). Pollen quantity is abundant.Pollen color is yellow (Fan #1, Sheet 13-A). ‘D6N-72’ is self-fertile.Pollination tests indicate that ‘D6N-72’ does not need cross-pollinationin order to set a commercial crop.

Stamens

The stamens are variable in length, from 7 to 11 mm. The stamens areusually shorter in length than the pistil. Filament color is white (Fan#4, Sheet 155-D).

Pistil

Pistil length ranges in length from 12 to 14 mm, including the ovary.The upper (distil) portion of the style is pale green in color (Fan #3,Sheet 150-D). The basal portion of the style and the ovary are darkergreen (Fan #3, Sheet 149-D). The surface of the upper portion of thestyle is glabrous. At times, a few fine hairs can be found on the lowerportion of the style and over the upper surface of the ovary.

Disease Resistance

‘D6N-72’ does not appear to be more or less susceptible to disease thanthe parent French variety.

DETAILED DESCRIPTION OF THE INVENTION

The breeding strategy of the program to develop the ‘D6N-72’ can beseparated into four distinct phases each having an individual purposeand crossing method. The first phase involved progeny testing of prunecultivars which historically have shown adaptation to California growingconditions. Open pollinated seedling populations derived from eachcultivar were screened with the standard fruit evaluation andindividuals were identified that expressed precocity of bearing(shortened juvenility), spread of maturity (both early and late),freedom from heat damage (in both fruit and tree) and vigorous seedlinggrowth.

The superior seedlings from Phase 1 were advanced as parents into Phase2 and Phase 3 hybridization. The purpose of the second phase was toincrease the diversity of the germplasm by breeding cultivars that hadpositive characteristics but had not been used in California production.Superior seedlings possessing commercial cultivar characteristics can beidentified at any point in this program. In Phase 3, ‘Improved French’is being utilized as a common parent in a “backcross” breeding method.This phase uses superior seedlings identified in Phase 1 and Phase 2 asparents and crosses them to a single common parent, ‘Improved French.’This “backcross” breeding method generally produces seedling populationsthat contain at least 50% “French” genome and have a high potential forproducing fruit similar to “French” on vigorous, precocious andproductive trees. The fourth phase of the breeding program involvesfurther breeding and selection of the superior seedlings from Phases 2and 3 for disease and pest resistance.

Pollination and Seedling Cultivation

The annual workings of the breeding program begin at pollination. Apollination list is planned by selecting the parents from the topselected items that show the potential of becoming new cultivars andfrom the items that have been selected on their breeding potential butlack the potential of becoming cultivars themselves. Flowers from thepollen parent are collected from the trees at the popcorn stage ofbloom. The fully closed flowers are removed from the trees and thestamens are separated by rubbing the flowers over a clean screen. Thestamens are dried at ambient temperature to release the pollen. Thepollen is stored in vials in a refrigerator. Limbs of the seed parentsare chosen for crossing when the flowers have reached 40-50% of fullbloom. All of the open flowers are removed from the limbs and discarded.The remaining closed flowers are emasculated (petals and stamens areremoved) with tweezers, leaving only the pistil and ovary attached tothe tree. The collected pollen is placed on each individual pistil ofthe selected limbs. Five hundred to fifteen hundred flowers arepollinated for each desired cross to ensure a moderately sized progenyfamily. The large numbers of pollinations are needed because fruit setcan be variable due to a variety of factors; poor weather, pollennon-viability, parental incompatibility, and manual damage. The fruitsformed by the pollinations are left to mature on the tree until about 10days before fruit ripening.

Seedling culture is the care of the seedlings from seed to nursery. Thefirst step is the collection of the fruit from the pollinations. Thefruit is stored at 32° F. until the time of seed removal. The seed isremoved from the fruit in early fall and placed in plastic bags withmoist paper towels that contain antibiotics and fungicide. The seed isthen stratified for 2 months at 37-45° F. After stratification the seedcoats are peeled off each seed to remove any growth inhibitors thatmight still be present. The peeled seed is planted in cones filled withpotting soil. The planted cones are placed in a greenhouse where theygerminate under mist. The mist is removed after germination is complete.The seedlings grow in the greenhouse with ample light, heat, andnutrients until their stems have begun to harden and are about 12 inchestall. They are then acclimatized in a lathhouse before being planted ina seedling nursery. At the end of the first growing season, theseedlings are undercut and then planted in high density seedling blocksat the University of California Davis campus research orchards.

Field Testing

Field testing and evaluation of prune selections such as ‘D6N-72’ arecarried out generally at several levels.

Initial testing involves evaluations made in the seedling blocks locatedat UC Davis and the selections blocks at Kearney, Calif. and Winters,Calif. Initial fruit evaluation is made on the original self-rootedseedlings in the high density seedling blocks. When enough fruit isavailable on a seedling for preliminary data collection and a positiveevaluation has resulted, the seedling becomes a “selection” and is thenconsidered for repropagation in prune selection blocks located at theKearney Agricultural Center—Parlier, Calif. and at the WolfskillExperimental Orchard at Winters, Calif. Depending on the perceivedpotential of the individual selection, from two to four trees of any oneselection are established on commercial rootstock. Variations in fruitsize, tree vigor, maturity date and other characteristics may, and oftendo, occur when the selection is moved onto a rootstock from the originalseedling. Most individual selections are refruited in the selectionblocks prior to advanced testing with growers.

Subsequent testing involves the establishment of advanced selections ingrower orchards in various prune growing locations. Again, depending onthe perceived value of the individual item, from two to fifty trees ofany one selection are established at any one location. Grower tests areestablished in counties throughout the Sacramento and San JoaquinValleys in California where prunes are a commercial crop.

Further testing involves the planting of small test acreage, usually ofa single targeted selection. The size of these further tests depends onthe apparent potential of the individual selection and the level of riskthat the cooperating grower wishes to assume. Planting size ranges fromtwenty five up to several hundred trees. Commercial value of an item canbe established in test markets with the expanded production of thisfurther testing.

Selection and Evaluation

Selection and evaluations begin with the first time the seedlings bloom.The tree is noted for precocity and is checked later to see if itsuccessfully set fruit. When a seedling sets its first sizable crop, thefruit is evaluated in the field setting. Maturity date, tree vigor, cropload, fruit size, fruit color, internal flesh quality, pit size, pittype (cling or free), fresh taste, and external flaws are recorded.During this first evaluation, trees can be discarded on the basis of anyof these characteristics, except for crop load which is usually onlyused as a disqualifier after several years of cropping. Some examples offirst year disqualifiers are high acidity or astringency, extremelytight pit, large pit size, split pits, gas pockets, lack of firmness inflesh, green or mottled color, small fruit size, deep sutures, cracks onside or ends, heat damage, russet scab, and early fruit drop.

If the field evaluation of a seedling is positive and the fruit qualityshows potential, a sample of ten fruit is collected and a secondaryfresh evaluation is done in the laboratory. This evaluation is done onthe same day as the field evaluation. The fruit is weighed and theaverage fruit weight (g) is recorded. The maturity of the fruit isestimated by pressure testing the flesh of the ten fruit and recordingthe average (PSI). The soluble solids are sampled by taking half of eachfruit and pulverizing them together in a blender then examining theclear juice with a refractometer. This method establishes the averagesoluble solids (Brix) of the sample. Again, taste and any exterior orinternal flaws are recorded. If the sample shows a high soluble solidscompared to other samples at that ripening date and the flavor and fruitquality are above average then a larger sample is collect from theseedling for test drying. If the sample shows low soluble solids or poorfruit quality then the seedling is either marked for discard orevaluation in the next year.

The next step in the evaluation system is to test dry the harvestedsamples. A dehydrator such as Harvest Saver dehydrator, built byCommercial Dehydrator Systems, Inc., may be utilized to dry the fruit.The samples are placed in net bags and washed before drying. They aredried for two hours at 185° F. after which the temperature is lowered to165° F. for the remaining time. Samples are dried between 18 to 24 hoursdepending on filled drier capacity and individual samplecharacteristics. The prune samples are weighed before and after dryingand the fresh to dry ratio is calculated. The dried fruit count perpound is also recorded. The prune samples are stored at 32° F. until thelate fall when the final evaluation takes place.

The last evaluation for the year is the rehydrated or processedevaluation. The prune samples are rehydrated by submerging the fruit inwater that is between 185-203° F. for six to eight minutes. Therehydrated prunes are placed in a plastic bag and stored in arefrigerator until their moisture content has equalized. The processeddried plums are evaluated. They are evaluated for fruit size, fruitcolor, color uniformity, surface wrinkles, skin peel, surfacebrightness, fruit shape, pit size, pit adherence, flesh color, fleshquality, and taste. Taste and appearance play a large role in theadvancement of a seedling selection. Items are discarded if any of thesetraits do not equally compare to or exceed the standards set by thecultivar, ‘Improved French’.

The evaluations described above take place at all levels of testing. Theemphasis on individual traits changes at each level. In early testing,more emphasis is given to the actual fruit characteristics during theprocessed evaluation. In later testing the whole tree characteristicsare emphasized, such as time of maturity over varying environments,annual bearing habits, crop load, and tree structure.

‘D6N-72’

As detailed above, ‘D6N-72’ (‘Improved French’×‘Tulare Giant’) is a highquality drying plum with a fruity flavor and thick meaty flesh. This newcultivar has been identified utilizing the above described selection andevaluation procedure.

The maturity date of ‘D6N-72’ falls approximately ten to fifteen daysbefore the industry standard ‘Improved French’. The size of the fruitaverages 40 grams fresh weight with an average soluble solids between21.0-24.0 degrees brix. The fruit is an oval shape, without a neck. Apurple-rose skin color covers the entire fruit at maturity. The flesh isa golden orange and retains the golden color after drying. The fruitdries without slabing or bleeding and the pit remains semi-free. Theresults of a pitting trial show that the pit comes free of the flesh andthe processed fruit is of high eating quality. The shape of the driedfruit is flatter than “French.” The flatness of ‘D6N-72’ may be due tothe drying process and not a fruit quality in itself.

The harvest data of ‘D6N-72’ in comparison to Sutter and French areshown in Table 1.

TABLE 1 Harvest Data Summary of the Advanced Selections Harvest DaysSoluble Fruit Crop Selection Date From Solids % Size (ct/lb) Load“French” ‘D6N-72’ Aug. 8, 2002 −12 days 23.6 36 Med Sutter Aug. 14, 2002 −9 days 30.8 39 Light (WEO) French Aug. 22, 2002  0 days 28.9 35 Light(WEO)

1. A new and distinct prune tree, ‘D6N-72’, substantially as describedand illustrated herein.